X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=773bc5508d3bdf513b29e622b9067789abf36b06;hp=07fa162bbd87d6f26e561f51b59d3fe4bac76d1e;hb=b822542608326092e177fd1707ca7fb53b2846c4;hpb=cee360d32efd8392f7e342dcaeda1de50a2c1bcf

diff --git a/README b/README
index 07fa162bb..773bc5508 100644
--- a/README
+++ b/README
@@ -1,37 +1,57 @@
+udev - userspace device management
 
-udev - a userspace implementation of devfs
+For more information see the files in the docs/ directory.
 
-For more information on the design, and structure of this project, see the
-files in the docs/ directory.
+Important Note:
+  Integrating udev in the system has complex dependencies and differs from distro
+  to distro. All major distros depend on udev these days and the system may not
+  work without a properly installed version. The upstream udev project does not
+  recommend to replace a distro's udev installation with the upstream version.
 
-To use:
+Requirements:
+  - Version 2.6.22 of the Linux kernel for reliable operation of this release of
+    udev. The kernel must not use the CONFIG_SYSFS_DEPRECATED* option.
 
-- Edit the udev.h file and replace the following variables with values
-  that make sense for your system:
-	#define UDEV_ROOT       "/udev/"
-	#define MKNOD           "/bin/mknod"
-  The only value most people will have to change is the UDEV_ROOT
-  variable, as I doubt you really want device nodes to be created in my
-  home directory :)
+  - The kernel must have sysfs, unix domain sockets and networking enabled.
+    Unix domain sockets (CONFIG_UNIX) as a loadable kernel module is not
+    supported.
 
-- Run make to build the project.
+  - The proc filesystem must be mounted on /proc/, the sysfs filesystem must
+    be mounted at /sys/. No other locations are supported by udev.
 
-- Make sure sysfs is mounted.
+  - The system must have the following group names resolvable at udev startup:
+      disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, kmem.
+    Especially in LDAP setups, it is required, that getgrnam() is able to resolve
+    these group names with only the rootfs mounted, and while no network is
+    available.
 
-- Point /proc/sys/kernel/hotplug at the location of the udev binary that
-  is created.  Then plug some block devices in, or other types of
-  devices that create dev files in sysfs.  An easy way to do this,
-  without any hardware is to use the scsi_debug module to create virtual
-  scsi devices.
+Operation:
+  Udev creates and removes device nodes in /dev/, based on events the kernel
+  sends out on device discovery or removal.
 
-- Watch as the nodes get created and removed.
+  - Very early in the boot process, the /dev/ directory should get a 'tmpfs'
+    filesystem mounted, which is populated from scratch by udev. Created nodes
+    or changed permissions will not survive a reboot, which is intentional.
 
+  - The content of /lib/udev/devices/ directory which contains the nodes,
+    symlinks and directories, which are always expected to be in /dev, should
+    be copied over to the tmpfs mounted /dev, to provide the required nodes
+    to initialize udev and continue booting.
 
-Yes this is a really rough first cut, I know.  It's mostly a proof of
-concept that this can actually work.  See the TODO file for a list of
-things left to be done.
+  - The old hotplug helper /sbin/hotplug should be disabled on bootup, before
+    actions like loading kernel modules are taken, which may cause a lot of
+    events.
 
-Any comment/questions/concerns please let me know.
+  - The udevd daemon must be started on bootup to receive netlink uevents
+    from the kernel driver core.
+
+  - All kernel events are matched against a set of specified rules in
+    /lib/udev/rules.d/ which make it possible to hook into the event
+    processing to load required kernel modules and setup devices. For all
+    devices the kernel exports a major/minor number, udev will create a
+    device node with the default kernel name, or the one specified by a
+    matching udev rule.
+
+Please direct any comment/question/concern to the linux-hotplug mailing list at:
+  linux-hotplug@vger.kernel.org
 
-greg k-h
-greg@kroah.com